So apparently Pakistan blocking Youtube is what affected the rest of the world (I kid you not).

What happened was that an ISP in Pakistan called "PieNet" uploaded new routing tables so that routes to Youtube would not go through. It is not known for certain how they managed to "poison" the rest of the Internet. I can say for sure that anybody inside or outside of Pakistan that was routed through them would have definitely been blocked, but apparently the scope reached other parts of the world too.

As a result, the world wide telecom that handles most of Pakistan's Internet traffic (PPCW Global) has taken all of Pakistan COMPLETELY OFFLINE!

Edit - Ok so I've been reading up on this because it's an area that interests me. For those who have no idea how the hell one small ISP in Pakistan was able to block a web site for the whole world, and how susceptible the Internet is to this kind of "attack" then read up on the Border Gateway Protocol: